Digital Signal Processing Reference
In-Depth Information
unoptimized Lazy ZF
BER-optimized Lazy ZF
BER and ZF-Optimized
10
-1
10
-3
10
-5
10
-7
10
-9
10
20
30
40
50
60
Signal power p
0
in dB
10
1
10
0
Lazy ZF
ZF-MMSE
10
-1
10
-2
10
-3
10
20
30
40
50
60
Signal power p
0
in dB
Figure 11.12
. Comparison of the lazy precoder with the optimal precoder, both
under the zero-forcing constraint. Shown are the average error probability plot (top)
and MSE per symbol (bottom). A 2-bit PAM constellation is assumed.
M
=16and
σ
s
=1
.
The diagonal channel in Fig. 11.8 is used.
Example 11.4: Lazy precoder versus optimal precoder
Consider again the channel
{H
k
/σ
q
k
}
shown in Fig. 11.8 (top). In this example
we assume
M
=16
,σ
s
=1
,
and a 2-bit PAM constellation. With a zero-
forcing equalizer assumed in Fig. 11.11, the minimized probability of error (using
the unitary matrix
U
) is plotted in the top of Fig. 11.12 (solid curve). For
comparison the plot also shows the performance of the ZF-MMSE system, which
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